Over the years, there have been many proposals for applying braking action to the wheels of a trailer or other towed vehicle. Many of these systems have utilized hydraulic braking action, similar to standard braking systems on automotive vehicles. However, in spite of substantial technical advances in automotive type systems, few true advances in technology have occurred for these trailer braking systems. With today's highway traffic safety regulations becoming more and more stringent, improved braking for trailers is becoming a necessity.
At the present time, the most widely used trailer braking system is an electro-mechanical system that is activated by the rearward force transmitted to the tongue of the trailer when the brakes of the towing vehicle are applied. A mechanical transducer senses the force along the tongue and, in turn, activates the brake cylinders to apply hydraulic pressure to the brake pads. The hydraulic pressure is actually generated by a master cylinder integral with or mounted on the trailer tongue.
In order to permit backing of the trailer, these systems that are in wide use today include an electrical solenoid for rendering the hydraulic system ineffective. This disabling action takes place in response to activation of the backup lights of the towing vehicle. Of course, because of this feature, an electrical connection must be made between the backup lights and the solenoid each time the trailer is hitched to the towing vehicle.
In addition to the requirement to make this connection being inconvenient, it has been found in practice that the electrical coupling is often damaged, such as by inadvertent tugging on the wires, and during the long periods of non-use, due to such factors as weather-related corrosion of the electrical contacts. In addition to likely malfunction of the trailer braking system, this added electrical load and the possibility of a short sometimes causes malfunction in the towing vehicle's electrical system. Furthermore, if the driver forgets to make the electrical connection or the connection is faulty, substantial damage can be done to the trailer upon backing when the brakes engage. Under possible extreme conditions, the trailer can be caused to jackknife and even overturn due to the brakes grabbing and locking up. An example in the prior art of this type of electro-mechanical braking system is shown in the Gatt U.S. Pat. No. 3,754,623, issued Aug. 28, 1973.
Competitors of the electro-mechanical braking system have attempted to solve these problems, and others, by converting to a fully hydraulically operated apparatus. A representative patent showing this type of system is the Jewell U.S. Pat. No. 3,746,132, issued Jul. 17, 1973. This type of system has not gained acceptance due to various shortcomings, but due mainly to an inefficient manner of mounting the brake assembly on the wheel spindle on the towed vehicle.
Also, the activation and deactivation of the brakes in the Jewell type system has in the past been generally unreliable due, in part, to the reliance on slotted mounts to provide relative movement for activation of the release valve unit, and in general unstable mounting of the valve unit. Buildup of road dirt and debris between the moving surfaces and in the open slots has proven to contribute to inefficient operation. These problems have in effect been instrumental in leading the industry to accept the electro-mechanical systems of the type shown in the Gatt '623 patent, along with its shortcomings as described above.